Electromagnetic flowmeter

ABSTRACT

An electromagnetic flowmeter comprising a conduit of nonmagnetic material for passing therethrough a liquid to be measured, a permanent magnet of cylindrical shape mounted on the outer circumferential surface of said conduit in concentric relationship, two radial openings formed in two positions diametrically opposed to each other on said permanent magnet in substantially the central portion axially of the magnet, two electrodes mounted in said two radial openings respectively, and external magnetic field shield means mounted around said permanent magnet in enclosing relationship.

United States Patent Tetsuya Sato No. 34 4-Chome, Hirano, Shinga-cho,Ibos l'laruo Mlyatake, No. 2417 Kaneoka-cho, Sakai; ()samu Kato, N0. 50,2-Ch0me, Natsato-cho, Nlshujodogawa-ku, Osaka [721 Inventors all ofJapan [21] Appl. No. 54,823 [22] Filed July 14, 1970 [45] Patented Jan.4, 1972 [32] Priority July 24, 1969 J p [31] 44/69803 [54]ELECTROMAGNETIC FLOWMETER 3 Claims, 4 Drawing Figs.

[52] U.S. Cl 73/194 EM [51] Int. Cl G0lp 5/08 [50] Field ofSearch..73/194 EM;

[56] References Cited UNITED STATES PATENTS 2,149,847 3/1939 Kolin73/194 EM 2,907,207 10/1959 Rinia 73/194 EM 3,095,744 7/1963 Hutchins eta1. 73/194 EM 3,339,410 9/1967 Steru 73/194 EM Primary Examiner-CharlesA. Ruehl Att0rney-Stevens, Davis, Miller & Mosher ABSTRACT: Anelectromagnetic flowmeter comprising a conduit of nonmagnetic materialfor passing therethrough a liquid to be measured, a permanent magnet ofcylindrical shape mounted on the outer circumferential surface of saidconduit in concentric relationship, two radial openings formed in twopositions diametrically opposed to each other on said permanent magnetin substantially the central portion axially of the magnet, twoelectrodes mounted in said two radial openings respectively, andexternal magnetic field shield means mounted around said permanentmagnet in enclosing relationship.

ELECTROMAGNETIC FLOWMETER This invention relates to flowmeters formeasuring the rate of fiow of a liquid metal. More particularly, theinvention is concerned with an electromagnetic fiowmeter adapted for usein measuring the flow rate of mercury when caustic soda is produced byelectrolysis of the mercury method.

Present practice in the determination of a flow rate of mercury passedthrough an electrolytic cell used for producing caustic soda byelectrolysis of the mercury process requires collection of specimens ofmercury from the upper portion and lower portion of the cell fordetermining the flow rate by calculation from a variation in theconcentration of amalgam of sodium and the electric current used forelectrolysis. There are individual variations in the values obtained bythis method, and the process requires additional labor and is timeconsuming. The results obtained by this process is 1-5 percent accurate.In special cases, a process using a triangular weir or a square weir isemployed but this is not practical because expensive mercury is consumedin large quantities. A flowmeter of the orifice differentialpressure-type has a disadvantage in that a slight wear caused by a flowof mercury markedly lowers the accuracy of results, so that it is notfit for use in commercial operation.

Electromagnetic flowmeters of the prior art have a disadvantage in thatthey have a high rate of occurrence of leakage flux. They are large insize and consequently heavy in weight.

The present invention obviates the aforementioned disadvantages ofelectromagnetic flowmeters of the prior art.

Accordingly, the present invention has as its object the provision of anelectromagnetic flowmeter which is highly accurate and dependable inmeasuring operation, solid in structure, and low in cost.

Additional objects as well as features and advantages of the inventionwill be evident from the description set forth hereinafter whenconsidered in conjunction with the accompanying drawing, in which:

FIG. 1 is a front view, with certain parts being cut out, of theelectromagnetic flowmeter embodying the present invention;

FIG. 2 is a sectional view taken along the line IIll of FIG.

FIG. 3 is a longitudinal sectional view of a flowmeter of the prior art;and

FIG. 4 is a diagram showing the relation between flow rate and producedvoltage.

An embodiment of the present invention will now be explained withreference to the accompanying drawing. In FIG. I and FIG. 2, theelectromagnetic flowmeter according to this invention comprises aconduit 1 made of nonmagnetic metal for passing a stream of liquid metaltherethrough which has a lining 2 of a corrosion resistant electricallyinsulating material. A permanent magnet 5 made in one piece incylindrical shape or two pieces each in semicylindrical shape is mountedon the outer circumferential surface of the conduit 1 in concentricrelationship and held in place by a retainer frame 4 of a nonmagneticmaterial which is secured to the outer circumferential surface of themagnet 5 by bolts 6 and nuts 7. The permanent magnet 5 is formed withtwo radial openings 8, 8 disposed in positions diametrically opposed toeach other in substantially the central portion axially of the magnet.Two electrodes 9, 9 are mounted in the openings 8, 8 respectively.External magnetic field shield means 10 comprising a number ofcylindrical shields made of soft steel is mounted around the permanentmagnet 5 in enclosing relationship in such a manner that the cylindricalshields are disposed concentrically with the magnet 5 and with eachother with a small clearance being disposed between the cylindricalshields. The external magnetic field shield means 10 is secured to theconduit 1 by bolts 11 and nuts 12. Another external magnetic fieldshield means 10' comprising a number of annular shields is mounted atopposite ends of the cylindrical shields 10 in juxtaposed relation withthe opposite ends of the cylindrical magnet 5 with a clearance betweenthe innermost annular shields 10' and the opposite ends of the magnet 5.The annular shields 10' are spaced apart from one another a smalldistance.

Connected to the electrodes 9, 9 are wires l3, l3 respectively fortransmitting to an amplifier and indicator section a DC voltage inducedin the electrodes which is in linear proportion to the rate of flow of aliquid metal through the conduit l.

Heretofore, a conventional fiowmeter of the permanentmagnet-type hasgenerally consisted of magnetic steel members l4, l4, pole pieces 15 andyoke 16 as shown in FIG. 3. The flowmeter of this type has adisadvantage in that leakage flux B markedly reduces the density of mainflux C. The provision of a uniform magnetic field requires the use ofrelatively large pole pieces l5, 15, which in turn causes a furtherreduction in the density of the main flux C. The conventional flowmeterof the type described is inevitably large in size and heavy in weight,and moreover it is high in cost in view of difficulty in working on andassembling parts.

The electromagnetic fiowmeter according to this invention is very simplein construction because the cylindrical magnet 5 formed in one piece ortwo pieces is held by the nonmagnetic retainer frame 4. In spite of itssimple construction, the flowmeter according to this invention producesa magnetic field having a high uniformity as shown by magnetic lines offorce A in FIG. 2 and an intensity which is three to four times as highas the intensity of a magnetic field provided by a conventional magneticflowmeter by using magnetic steel of the same kind.

The electrodes 9, 9 can be mounted readily in the openings 8, 8 drilledin the magnet S. The present invention provides an electromagneticflowmeter of high accuracy and precision which is compact in overallsize, light in weight and low in cost.

The electromagnetic flowmeter according to this invention has been usedwith electrolytic cells operated on a commercial basis. It has beenascertained that the DC voltage induced in the electrodes is in linearproportion to the flow rate of mercury, and that the value indicated bythe meter is not influenced by variations in the external field. Theblack dots on or near a line in FIG. 4 have been obtained by plottingthe values indicated by the electromagnetic flowmeter according to thisinvention as abscissae against the values of fiow rate determined by anamalgam density measuring method.

From the foregoing description, it will be appreciated that theelectromagnetic flowmeter of this invention has many advantages. Themagnetic field formed by the permanent magnet of the electromagneticflowmeter according to this invention is not affected by a highlyintensive space magnetic field of several hundred Gausses which prevailin an installation for producing caustic soda by electrolysis of themercury process, by virtue of the external magnetic field shield means.Thus, the meter can indicate values which are free from error. Thefiowmeter according to this invention is low in cost, compact in overallsize, light in weight and durable. The output voltage of the flowmetercan be utilized for effecting flow control and operating a warningdevice. The magnet flowmeter according to this invention is thus of agreat industrial value.

What is claimed is:

1. An electromagnetic flowmeter comprising a conduit of nonmagneticmaterial for passing therethrough a liquid to be measured, a permanentmagnet of cylindrical shape mounted on the outer circumferential surfaceof said conduit in concentric relationship, two radial openings formedin two position diametrically opposed to each other on said permanentmagnet in substantially the central portion axially of the magnet, twoelectrodes mounted in said two radial openings respectively, andexternal magnetic field shield means mounted around said permanentmagnet in enclosing relationship.

2. An electromagnetic fiowmeter as defined in claim 1 wherein saidpermanent magnet in cylindrical shape is formed in two pieces each insemicylindrical shape.

3. An electromagnetic flowmeter as defined in claim 1 wherein saidexternal magnetic field shield means comprises a set of cylindricalshields and a set of annular shields, said cylindrical shields and saidannular shields being arranged such that the cylindrical shields areconcentric with said permanent magnet and the annular shields aredisposed at opposite ends of the cylindrical shields, said shields beingspaced apart from one another and from the permanent magnet by a smallclearance.

1. An electromagnetic flowmeter comprising a conduit of nonmagneticmaterial for passing therethrough a liquid to be measured, a permanentmagnet of cylindrical shape mounted on the outer circumferential surfaceof said conduit in concentric relationship, two radial openings formedin two positions diametrically opposed to each other on said permanentmagnet in substantially the central portion axially of the magnet, twoelectrodes mounted in said two radial openings respectively, andexternal magnetic field shield means mounted around said permanentmagnet in enclosing relationship.
 2. An electromagnetic flowmeter asdefined in claim 1 wherein said permanent magnet in cylindrical shape isformed in two pieces each in semicylindrical shape.
 3. Anelectromagnetic flowmeter as defined in claim 1 wherein said externalmagnetic field shield means comprises a set of cylindrical shields and aset of annular shields, said cylindrical shields and said annularshields being arranged such that the cylindrical shields are concentricwith said permanent magnet and the annular shields are disposed atopposite ends of the cylindrical shields, said shields being spacedapart from one another and from the permanent magnet by a smallclearance.